Grain-oriented electrical steel sheets containing Si and having a crystal orientation highly aligned in {110}<001> orientation (Goss orientation) or {100}<001> orientation (Cube orientation) are excellent in the soft magnetic property, so that they are widely used as a core material for various electric instruments used in a commercial frequency region. The grain-oriented electrical steel sheet used in such an application is generally required to be low in the iron loss W17/50 (W/kg) representing magnetic loss when it is magnetized to 1.7 T at a frequency of 50 Hz. Because, the efficiency of power generator or transformer can be largely improved by using a core material with a low W17/50 value. Therefore, it is strongly demanded to develop materials having a low iron loss.
The iron loss of the electrical steel sheet is represented by a sum of hysteresis loss depending on crystal orientation, purity or the like and eddy current loss depending on sheet thickness, size of magnetic domain or the like. As a method of reducing the iron loss, therefore, there are known a method wherein an integration degree of crystal orientation is enhanced to increase a magnetic flux density and reduce hysteresis loss, a method wherein eddy current loss is reduced by increasing Si content for enhancing an electrical resistance, decreasing a thickness of a steel sheet or subdividing magnetic domain, and so on.
As to the method of increasing the magnetic flux density among these methods of reducing the iron loss, for example, Patent Documents 1 and 2 disclose that when Ni is added and Sb is added within a given range in response to the addition amount of Ni in the production method of the grain-oriented electrical steel sheet using AlN as an inhibitor, an extremely strong suppression force is obtained against the growth of primary recrystallized grains and hence it is attempted to improve primary recrystallized grain texture and refine secondary recrystallized grains and also an average in-plane angle deviated from {110}<001> orientation toward rolling direction can be made small to largely reduce the iron loss.
As the method of decreasing the sheet thickness, there are known a rolling method and a chemical polishing method. The method of decreasing the thickness by chemical polishing largely lowers the yield and is not suitable in the industrial-scale production. Therefore, the rolling method is exclusively used as the method of decreasing the sheet thickness. However, when the sheet thickness is decreased by rolling, there are problems that secondary recrystallization in final annealing becomes unstable and it is difficult to stably produce products having excellent magnetic properties.
As to such problems, For example, Patent Document 3 proposes that when a thin grain-oriented electrical steel sheet is produced by using AlN as a main inhibitor and performing final cold rolling under a strong rolling reduction, an excellent value of iron loss is obtained by composite addition of Sn and Se and further addition of Cu and/or Sb, and Patent Document 4 proposes that when Nb is added in the production method of a thin grain-oriented electrical steel sheet having a thickness of not more than 0.20 mm, fine dispersion of carbonitride is promoted to strengthen an inhibitor and improve magnetic properties. Further, Patent Document 5 proposes a method for producing a thin grain-oriented electrical steel sheet by single cold rolling wherein a thickness of a hot rolled sheet is made thinner and a coiling temperature is lowered and a pattern of final annealing is controlled properly, and Patent Document 6 proposes a method wherein a grain-oriented electrical steel sheet having a thickness of not more than 0.23 mm is produced by single cold rolling when a sheet thickness of a hot rolled coil is made to not more than 1.9 mm.